Bill Gates' energy innovation vehicle and the EU have teamed up at COP28 to fund green tech projects in Europe, including a trailblazing “CO2 battery” storage system in Italy.

Breakthrough Energy Catalyst – set up by Microsoft billionaire Gates to back promising energy technologies – has pledged up to €35m ($38m) for the “first-of-a-kind” project being developed by Italian start-up Energy Dome.

That is part of its wider “EU-Catalyst partnership” with the European Commission that will see Breakthrough pour €240m into EU green tech projects.

As part of that arrangement, the Commission has teed up the European Investment Bank (EIB) to make €25m venture debt financing commitment to Energy Dome.

Mario Fernandez, Head of Catalyst at Breakthrough Energy, said the announcement shows the “tangible impact” of its approach to “fund impactful projects that can move us closer to an emissions-free future.”

Energy Dome has developed a thermodynamic liquid-CO2 system to store excess green energy from wind and solar farms.

The system sees CO2 compressed until the gas is heated up to 300°C liquid. Heat is then extracted and stored “bricks” made of steel shot and quartzite for later use, cooling down the CO2 to an ambient temperature. The gas is then condensed into liquid form and stored in carbon-steel tanks.

When power is needed, the liquid CO2 is run through an evaporator to turn it back to a pressurised gas. This is re-heated before going through an expansion turbine, where it rapidly expands at atmospheric pressure to drive a power-generating rotor.

The uncompressed CO2 is then stored in a flexible dome — hence the company name — at ambient temperature and pressure for later re-use.

The project Breakthrough and the EIB are funding is the first commercial-scale battery that Energy Dome will have developed. It will be based near the commune of Ottana on the sun-drenched Mediterranean island of Sardinia.

The project will use a 20MW/200MWh CO2 battery, which can supply energy for ten hours straight. It will be the first of a series of identical units using the same design, which Energy Dome says will help it reduce costs going forward.

Claudio Spadacini, founder and CEO of Energy Dome, said: “What better time than during COP28 to announce the collaboration with the EU-Breakthrough Energy Catalyst partnership, which is a true catalyst for our company.”

EIB vice president Gelsomina Vigliotti said this is an “inspiring example of game-changing technology that we need more of in Europe and worldwide.”

The EU-Catalyst partnership is also backing a project by renewables developer Orsted to build the largest e-Methanol plant in Europe. Catalyst will take a 15% stake in the FlagshipONE project.

In total, the partnership plans to mobilise up to €840m of public and private funds to accelerate the deployment of emerging climate technologies.